cifs: add function to get a tcon from cifs_sb

When we convert cifs to do multiple sessions per mount, we'll need more
than one tcon per superblock. At that point "cifs_sb->tcon" will make
no sense. Add a new accessor function that gets a tcon given a cifs_sb.
For now, it just returns cifs_sb->tcon. Later it'll do more.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 84979fc..6712c2b 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -235,7 +235,7 @@
 	xid = GetXid();
 
 	cifs_sb = CIFS_SB(inode->i_sb);
-	tcon = cifs_sb->tcon;
+	tcon = cifs_sb_tcon(cifs_sb);
 
 	pCifsInode = CIFS_I(file->f_path.dentry->d_inode);
 
@@ -345,7 +345,7 @@
 		goto out;
 	}
 
-	if (cifs_sb->tcon->ses->capabilities & CAP_NT_SMBS)
+	if (tcon->ses->capabilities & CAP_NT_SMBS)
 		rc = CIFSSMBOpen(xid, tcon, full_path, disposition,
 			 desiredAccess, CREATE_NOT_DIR, &netfid, &oplock, buf,
 			 cifs_sb->local_nls, cifs_sb->mnt_cifs_flags